As a measure to obtain high output power, that is, strong striking force, from a hydraulic hammering device, attempts to increase the number of strikes have been carried out. To achieve a high number of strikes, a hammering method that controls hydraulic pressurized oil so as to switch each of a front chamber and a rear chamber of a piston into communication with either a high pressure circuit or a low pressure circuit in an interchanging manner (hereinafter, also referred to as “piston front/rear chamber high/low pressure switching type”) is effective. That is, a hydraulic hammering device of the piston front/rear chamber high/low pressure switching type does not cause hydraulic oil on the front chamber side to resist movements of the piston in the striking direction. Thus, a hydraulic hammering device of the piston front/rear chamber high/low pressure switching type is suitable for achieving a high number of strikes.
As a hydraulic hammering device of this type, for example, a technology described in JP 46-001590 A has been disclosed. As illustrated in a schematic view in FIG. 9, a hammering device of the piston front/rear chamber high/low pressure switching type described in PTL 1 includes a piston 520 that has large-diameter sections 521 and 522, which are disposed in the axially middle portion thereof, and small-diameter sections 523 and 524, which are formed in front and the rear of the large-diameter sections, respectively. The piston 520 being disposed in such a way as to be slidably fitted into the inside of a cylinder 500 causes a piston front chamber 501 and a piston rear chamber 502 to be defined inside the cylinder 500 individually. In the middle between the piston large-diameter sections 521 and 522, an oil discharge groove 525 is formed. A description will be made herein by defining a hammering direction (the left direction in the drawings) as “front”.
To the piston front chamber 501, a piston front chamber passage 506 is connected that communicates the piston front chamber 501 with either a high pressure circuit 538 or a low pressure circuit 539 depending on switching of a valve 526, which will be described later, between an advance and a retraction. On the other hand, to the piston rear chamber 502, a piston rear chamber passage 507 is connected that communicates the piston rear chamber 502 with either the high pressure circuit 538 or the low pressure circuit 539 depending on switching of the valve 526 between an advance and a retraction. The high pressure circuit 538 and the low pressure circuit 539 are provided with a high pressure accumulator 540 and a low pressure accumulator 543, respectively.
In the rear of the piston front chamber 501, a piston advance control port 503 is formed separated from the piston front chamber 501 at a predetermined interval, and, in front of the piston rear chamber 502, a piston retraction control port 504 is formed separated from the piston rear chamber 502 at a predetermined interval. The piston advance control port 503 has opening sections, which are intended for movements with a normal stroke and a short stroke, at two positions, and a piston advance control port 503a located on the piston front chamber 501 side is provided with a variable choke and is intended for a short stroke movement. A description will be made herein under an assumption that the piston advance control ports 503 and 503a are set to the normal stroke, that is, the variable choke is set to a full close state, and the piston advance control port 503 on the piston rear chamber 502 side works.
In the rear of the piston advance control port 503, a piston retraction control interlocking port 508 is formed separated from the piston advance control port 503 at a predetermined interval. In front of the piston retraction control port 504, a piston advance control interlocking port 509 is formed separated from the piston retraction control port 504 at a predetermined interval. Between the piston retraction control interlocking port 508 and the piston advance control interlocking port 509, an oil discharge port 505 is formed separated from both the piston retraction control interlocking port 508 and the piston advance control interlocking port 509 at predetermined intervals. Further, the piston advance control port 503 and the piston retraction control interlocking port 508 are in communication with a valve rear chamber 511 by way of a valve control passage 518, which will be described later, and the piston retraction control port 504 and the piston advance control interlocking port 509 are in communication with a valve front chamber 510 by way of a valve control passage 517, which will be described later.
In the cylinder 500, a valve chamber 541 is formed in a non-concentric manner with the piston 520, and a valve 526 is slidably fitted into the valve chamber 541. In the valve chamber 541, in order from the front to the rear, the valve front chamber 510, a valve retraction hold chamber 515, a main chamber 542, a valve advance hold chamber 516, and the valve rear chamber 511, are formed by annular steps. In the main chamber 542, a piston front chamber low pressure port 512, a piston high pressure port 514, and a piston rear chamber low pressure port 513 are disposed separated from each other at predetermined intervals from the front to the rear. To the intermediate section between the piston front chamber low pressure port 512 and the piston high pressure port 514 and the intermediate section between the piston high pressure port 514 and the piston rear chamber low pressure port 513, the piston front chamber passage 506 and the piston rear chamber passage 507 are connected, respectively.
The valve 526 is a solid valve body (spool) that has large-diameter sections 527, 528, and 529, medium-diameter sections 530 and 531 formed in front and the rear thereof, a small-diameter section 532 formed in front of the medium-diameter section 530, and a small-diameter section 533 formed in the rear of the medium-diameter section 531. Between the large-diameter section 527 and the large-diameter section 528 and between the large-diameter section 528 and the large-diameter section 529, a piston front chamber switching groove 534 and a piston rear chamber switching groove 535 are formed, respectively, in an annular manner. The small-diameter section 532 and the piston front chamber switching groove 534 are in communication with each other by way of a communication passage 536, and the small-diameter section 533 and the piston rear chamber switching groove 535 are in communication with each other by way of a communication passage 537.
The valve 526 is slidably fitted into the valve chamber 541 in such a way that the small-diameter section 532, the medium-diameter section 530, the large-diameter sections 527, 528, and 529, the medium-diameter section 531, and the small-diameter section 533 are positioned in the valve front chamber 510, the valve retraction hold chamber 515, the main chamber 542, the valve advance hold chamber 516, and the valve rear chamber 511, respectively. The valve 526 performing advance or retraction movements causes the large-diameter section 527 to open or close the piston front chamber low pressure port 512, the large-diameter section 528 to make the piston front chamber passage 506 and the piston high pressure port 514 communicate with or shut off from each other and, at the same time, to make the piston rear chamber passage 507 and the piston high pressure port 514 communicate with or shut off from each other, and the large-diameter section 529 to open or close the piston rear chamber low pressure port 513.
When the piston front chamber passage 506 comes into communication with the piston high pressure port 514, pressure in a valve retraction hold chamber 515 becomes high. Conversely, when the piston rear chamber passage 507 comes into communication with the piston high pressure port 514, pressure in a valve advance hold chamber 516 becomes high. The pressure receiving area of the valve front chamber 510 is set larger than that of the valve advance hold chamber 516. Similarly, the pressure receiving area of the valve rear chamber 511 is set larger than that of the valve retraction hold chamber 515.
Next, an operation of the above-described hydraulic hammering device will be described with reference to FIGS. 10A to 10D. In FIGS. 10A to 10D, passages to which a high pressure is applied are illustrated by “hatching”.
When the valve 526 is switched to an advanced position, the piston high pressure port 514 comes into communication with the piston rear chamber passage 507, causing pressure in the piston rear chamber 502 to become high. On the other hand, since the piston front chamber low pressure port 512 is in communication with the piston front chamber passage 506 to cause pressure in the piston front chamber 501 to become low, the piston 524 advances. At this time, although pressure in both the valve front chamber 510 and the valve rear chamber 511 becomes low, pressure in the valve advance hold chamber 516 is high, causing the valve 526 to be held at the advanced position (see FIG. 10A).
Subsequently, when the piston 524 advances and the piston retraction control port 504 comes into communication with the piston rear chamber 502, pressure in the valve front chamber 510 becomes high. Since the pressure receiving area of the valve front chamber 510 is larger than that of the valve advance hold chamber 516, the valve 526 starts retracting. At this time, since the valve rear chamber 511 is in communication with the low pressure circuit 539 by way of the valve control passage 518, the piston retraction control interlocking port 508, and the oil discharge port 505, the valve 526 is able to retract without any problem (see FIG. 10B).
When it is assumed that a hydraulic circuit without the piston retraction control interlocking port 508 is used in a retraction phase of the valve 526 illustrated in FIG. 10B, since the piston large-diameter section 521 blocks the piston advance control port 503, the valve rear chamber 511 and the valve control passage 518 constitute a closed circuit, causing the valve 526 to be unable to retract. That is, it becomes clear that, when the valve front chamber 510 communicates with the high pressure circuit 538 by way of the piston retraction control port 504 and the piston rear chamber 502, the piston retraction control interlocking port 508 that communicates the valve rear chamber 511 with the low pressure circuit 539 by way of the oil discharge port 505 is indispensable to secure a retraction movement of the valve 526.
Immediately after the piston 520 has reached an impact point, the valve 526 completes switching to a retracted position thereof. When the valve is positioned at the retracted position, the piston front chamber 501 comes into communication with the piston high pressure port 514 to cause pressure in the piston front chamber 501 to become high, and the piston rear chamber 502 comes into communication with the piston rear chamber low pressure port 513 to cause pressure in the piston rear chamber 502 to become low, causing the piston 520 to turn to retraction. Although pressure in both the valve front chamber 510 and the valve rear chamber 511 becomes low, pressure in the valve retraction hold chamber 515 becomes high, causing the valve 526 to be held at the retracted position (see FIG. 10C).
When the piston 520 retracts to cause the piston advance control port 503 to come into communication with the piston front chamber 501, pressure in the valve rear chamber 511 becomes high, and, since the pressure receiving area of the valve rear chamber 511 is larger than that of the valve retraction hold chamber 515, the valve 526 starts advancing. At this time, since the valve front chamber 510 is in communication with the low pressure circuit 539 by way of the valve control passage 517, the piston advance control interlocking port 509, and the oil discharge port 505, the valve 526 is able to advance without any problem (see FIG. 10D). The valve 526 is switched to the advanced position again, and the above-described cycle is repeated to perform hammering.
When it is assumed that a hydraulic circuit without the piston advance control interlocking port 509 is used in an advance phase of the valve 526 illustrated in FIG. 10D, since the piston large-diameter section 522 blocks the piston retraction control port 504, the valve front chamber 510 and the valve control passage 517 constitute a closed circuit, causing the valve 526 to become unable to advance. That is, it becomes clear that, when the valve rear chamber 511 communicates with the high pressure circuit 538 by way of the piston advance control port 503 and the piston front chamber 501, the piston advance control interlocking port 509 that communicates the valve front chamber 510 with the low pressure circuit 539 by way of the oil discharge port 505 is indispensable to secure an advance movement of the valve 526.